Homicide is the killing of one human being by another.   Generally, the term homicide is used in common parlance to refer to noncriminal acts as well as the criminal act of murder. Though homicides are generally considered as crimes, under certain circumstances, homicides are considered justifiable. 

Homicides therefore are not always a crime and sometimes the law allows homicide by allowing certain defenses to criminal charges.  This includes cases where a person is killed to prevent the commission of a serious felony or to aid a representative of the law.  Law considers some homicides to be excusable, as when a person kills another in self-defense.  Self defence is taken as a defence when a person commits homicide to protect his or her own life from a deadly attack. 

Homicides conducted with state sanctions are also not considered as crimes.  The most obvious example is capital punishment.  Capital punishment is carried out in cases of persons when the state determines that a person should die.  Homicides committed in action during war are usually not subject to criminal prosecution either.  In addition, members of law enforcement entities are also allowed to commit justified homicides within certain parameters and these also do not usually result in prosecution.

Law makes distinctions between different types of homicide, and punishments vary greatly according to the intent of the killer, the dangerousness of his conduct, and the circumstances in which he acted.  Though there are different types of homicides, only criminal homicides are not regarded by the applicable criminal code as justifiable or excusable.